The yeast cell wall is composed of glucan, mannoprotein and chitin. In most yeasts and especially Saccharomyces, the polysaccharide glucan is predominantly .beta.-1,3-linked with some branching via .beta.-1,6-linkages. Several microorganisms have been reported to produce extracellular enzymes capable of lysing viable yeast cells. Analysis of the constituents of these lytic enzyme preparations revealed the presence, among other activities, of a .beta.-1,3-glucanase and a protease. When combined with a thiol reagent, .beta.-1,3-glucanase alone was found to be responsible for the yeast cell lysis function.
Several molecular forms of .beta.-1,3-glucanase have been identified in the culture supernatant of Arthrobacter species. While all of the observed molecular forms of the enzyme possessed hydrolytic activity towards .beta.-glucans (glucanase activity), only some were found capable of inducing lysis of viable yeast cells (lytic activity). It is not clear whether all of these species of glucanase are different native enzymes with different substrate specificities or, that the species deficient in the lytic function are products of proteolytic degradation of a single native enzyme containing both glucanase and lytic activity. Furthermore, presently available enzyme preparations for use in the lysis of yeast cells are unsatisfactory because they contain undesirable protease activity. Hence, it would therefore be desirable to provide a means for high level expression of a .beta.-1,3-glucanase gene in a heterologous host for subsequent purification of the enzyme without interference or copurification of the endogenous protease.
A single molecular species of .beta.-1,3-glucanase with lytic activity has been substantially but not completely purified away from the protease by Scott et al. (1980), J. Bacteriol. 142, 414-423, from the culture supernatant of Oerskovia xanthineolytica. On the other hand, Doi et al. (1986), J. Bacteriol. 168, 1272-1276, have succeeded in cloning into E. coli of a DNA fragment encoding a .beta.-1,3-glucanase activity taken from Arthrobacter sp. strain YCWD3. However, the level of .beta.-1,3-glucanase expression in E. coli from this cloned DNA fragment was low, and since its nucleotide sequence and location of the glucanase gene are not known, improving the expression level is difficult to achieve. Thus, incomplete removal of the protease and poor expression yields render the above systems unsuitable for any significant production of useful glucanase preparations.